2011-12-30

So now Opportunity is sitting in front of a rock known as Santa Catarina, ready to IDD the heck out of it. As has happened before -- and recently, too -- the target is heavily shadowed, so our terrain mesh is poor. There's a sort of "king's crown" of mesh spikes surrounding the rock and pointing toward the FHAZ.

This makes the whole day ... well ... interesting. Hand-estimating surface normals to the target is always dicey, and it's worse when you reflect that we can break the IDD if we're off by more than 15 degrees.

So that we won't have to do this tomorrow, we also make some time for swinging the IDD away and taking another FHAZ of the IDD workspace. If only the rover had fingers she could cross.

Meanwhile, Santa Catarina itself is an interesting rock. Well, not to me, maybe, but to the science team, and that's all it takes. According to Squyres, "Santa Catarina is the first rock we've seen at Meridiani where, a, we can say something about where on Mars it came from, and b, it's not made of blueberry stuff." Good news for them, then.

Another piece of good news is that I actually see improvement in Terry's IDD sequencing. Especially on a day like today, which is plenty stressful already.

I just hope I haven't spent all my luck on that. I'm going to need some left over for the FHAZ we're taking. Especially since Opportunity can't cross her fingers.

[Next post: sol 1068, January 4.]

Courtesy NASA/JPL-Caltech. Santa Catarina, in all its heavily shadowed glory. On the next rover, I want headlights, you hear me? Headlights!

2011-12-19

Yestersol's drive didn't go quite as planned. Opportunity drove through a small depression that increased her tilt to 7.44deg -- just above her tilt limit of 7deg -- so she stopped, which of course was the right thing to do. But she's actually fine, and ready to continue.[1]

The remainder of the drive is only about 8m, and that stops us in a perfectly safe position, about 2m from the rim. But there's a ritual now: any rim approach causes some people to panic, and after a lengthy discussion, we end up moving the final position back another 50cm. Which is how it always happens. It's just silly: we're not going to be wrong by 2m over a drive of 8m, and even if we were, we have reactive checks -- such as the tilt limit that correctly stopped us today -- that would catch our mistake before the vehicle was in danger. The 50cm pullback is just a compromise to end the discussion, nothing more.

What bugs me about this most, I think, is the fact that the extra 50cm of buffer is there not for any technical reason but to mollify the exaggerated concerns of people who aren't RPs. There, I said it. It feels good to have it said.

Tomorrow, no doubt, the ritual will be performed again.

[Next post: sol 1063 (Opportunity sol 1045), December 30.]

[1] One of the hazards of the job, I'm afraid. You always want to pick a tilt limit that's just a little higher than you think the rover will actually experience, so that an excessive tilt will mean she's strayed off course. But it doesn't always work like that: faulty data or other problems can lead you to choose a number that's lower than you should have. Fortunately, nearly all the time -- as in this case -- the problem with being overly conservative is just slight embarrassment. As long as I still have a rover to play with the next day, I can take it.

2011-12-05

Yestersol's Opportunity drive went well, so we're not going anywhere in particular today. Mostly, we're going to sit and take pictures.

But we are doing a bit of driving. In order to optimize our downlink for the weekend, we're just going to do a comm turn.

Steve Squyres raises an interesting issue with this. Back when we developed our strategies for driving with this IDD problem, one of the things we told NASA HQ was that we'd hover-stow (a.k.a. "thinker-stow") whenever possible, mostly to minimize the risk that the IDD would fail in the stowed configuration. However, we've kind of lost sight of that, preferring to do a full stow on every drive, because it's so much easier.

It is also, in more than one respect, safer. In order to drive in the thinker-stow position, we need to ensure that we don't drive any wheel over anything bigger than 3cm. Also, we can lose calibration when we do that, because the IDD bounces around more than when it's tucked safely below the rover's chest.

What ends up putting the kibosh on thinker-stowing for the day is not any of those considerations, but one more esoteric. The rover won't drive when it thinks the IDD is not stowed, and the thinker-stow position doesn't meet the rover's definition of a stow. So you have to poke a flag that tells it to consider the IDD stowed anyway. However, the command that does that hasn't been tested under the new flight software, and the potential downsides are significant. So we don't do it. I'll have to look into the matter soon and ensure that we can thinker-stow in the new FSW, but at least for today, things stay simple.

2011-12-03

And off we go. Our big goal for the day is just to turn from a heading of 167 to a heading of 270, the first piece of our Esperanza drive. If everything goes exactly as planned, we'll end up straddling the shelf that was off to our right when we were at Winter Haven. In the best case, we'll also try to bump about 1m back along the shelf, just to see how that goes -- but if it doesn't get a chance to run due to time constraints, that'll be fine with us.

Happily, we're up to a whopping 357 W-hr. Well, that really is whopping, for Spirit these days. That number keeps climbing, and as it does, we'll be able to move more and more. And as drives like this one build our confidence, I hope we'll be able to drive more and more confidently.